ABSTRACT
The biopollution assessment method was used to compare relative impacts of the zebra mussel (Dreissena polymorpha) across different regions (assessment units) in the Shannon River system, Ireland. The approach involved dening the zebra mussel abundance and distribution range, as well as the impact of this species on communities, habitats, and ecosystems based on surveys and studies over the period 1997-2007. Zebra mussels were found associated with most habitats ranging from rocky shallows to soft sediments in depths to 37 m. Abundance and biomass were greatest in lakes/reservoirs and lowest in rivers/ canals, and impacts were greatest in assessment units having mainly lentic characteristics. Impacts involved total losses of unionids, declines in chlorophyll, and increases in rooted aquatic macrophytes. Variation in the magnitude of impact within each assessment unit depended upon specic features such as pH, available calcium, and most probably turbulence.
